Oncorhynchus nerka

Non-anadromous (kokanee) and anadromous (sockeye) forms formerly were considered different subspecies; subsequent studies indicate that the two subspecies (nerka = sockeye; kennerlyi = kokanee) cannot be adequately separated. Sockeye and kokanee salmon in Redfish Lake, Idaho, likely are reproductively isolated (Williams et al. 1992).

Taylor et al. (1996) examined genetic variation among 24 populations ranging from Kamchatka to the Columbia River and identified two major genetic groups: a "northwestern" group (Kamchatka, western Alaska, northwestern British Columbia) and a "southern" group (sockeye and kokanee populations from the Fraser and Columbia river systems). "The populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity." "Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific." The authors concluded that "sockeye salmon and kokanee and para- and polyphyletic, respectively, and that the present distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye throughout the North Pacific."

Hendry et al. (2000) presented evidence suggesting that reproductive isolation between introduced populations of common origin can evolve after fewer than 13 generations.

This species is widespread and has many occurrences. Many subpopulations are declining and there are numerous, mostly localized threats, but evidence for a species-wide decline are not great enough to trigger a less secure global status rank.

During oceanic feeding and maturation, this salmon ranges throughout the North Pacific Ocean, Bering Sea, and eastern Sea of Okhotsk north of 40 degrees north latitude; there is considerable intermingling of Asian and North American populations, and of North American populations from Bering Sea and Gulf of Alaska streams; the range shifts southward for winter, northward during warmer months. Natural lake populations occur in Japan, former USSR, Alaska, Washington, Idaho, Oregon, Yukon, and British Columbia. Anadromous forms occur in Asia from Hokkaido, Japan, to the Anadyr River (spawning mainly on the Kamchatka Peninsula); in North America, anadromous populations range from the Sacramento River, California, north to Point Hope, Alaska (common in north, rare south of Columbia River drainage). Major Alaskan spawning areas are in tributaries and lakes of the Kenai, Chignik, Naknet, Kuichak, Wood, and Kodiak Island river systems. South of Alaska in the Pacific Northwest, the major spawning river is the Fraser River system in British Columbia, with smaller runs in the Baker, Columbia, Cedar, Quinalt, and Ozette rivers in Washington. The Fraser River includes a number of important nursery lakes (Cultus, Adams, Harrison, Horsefly, Shuswap, and Quesnel) and many tributaries that support the major portion of the Pacific Northwest population. In eastern Washington, major nursery lakes for Columbia River are Lake Wenathchee and Osoyoos Lake. In western Washington, major nursery lakes are Quinalt Lake, Ozette Lake, Baker Lake, and Lake Washington. In a 1996 survey of populations in the contiguous U.S., one healthy native stock was identified (Wenatchee River, Washington). The kokanee (lake-stream form) has been introduced in many western states and elsewhere, but most transplants have been unsuccessful in establishing self-sustaining populations.

At least 64 stocks are known from Alaska, British Columbia, and Washington (Peterman and Dorner 2012). Assuming each involves at least one occurrence and adding stocks from the remainder of the range, there are likely hundreds of occurrences of this wide-ranging species.

Threats to this species are dams that blocked migration, mainstem passage mortality at Columbia and Snake river dams, overutilization in commercial fisheries, and habitat modification (see Nehlsen et al. 1991). Sockeye in the Deschutes River (Oregon) were largely eradicated by dam construction (small anadromous run is maintained by incidental passage of smolts from a resident kokanee population) (Nehlsen et al. 1991). In the Puget Sound area, decline of the Baker River sockeye population has been attributed to upstream and downstream passage problems as a result of dam construction (Nehlsen et al. 1991). Lake Ozette sockeye run on the Washington coast declined because of logging and overfishing in the 1940s and 1950s (Nehlsen et al. 1991). Climate change is another threat, with most life stages affected by temperature (Martins et al. 2012).

The decline and persistent low abundance of the Rivers Inlet population in British Columbia apparently was due to poor marine survival, and not due to a decline in juvenile abundance (McKinnell et al. 2001).